1. Technical Field of the Invention
The present invention relates to a dial operation device having a knob dial to be rotated for operation.
2. Technical Background
FIGS. 7 and 8 are views showing a conventional structure of the above dial operation device. In this structure, there is provided a printed wiring board 1, onto which a support 2a of a knob base 2 is attached by screws. On an outer circumferential surface of the knob base 2, a knob dial 3 is pivotally engaged. A knob body 4 is engaged on an inner circumferential surface of the knob dial 3. Therefore, when the knob dial 3 is rotated for operation, the knob body 4 is rotated integrally with the knob dial 3.
In the knob body 4, there is formed a moderation surface 4a. Engaging pieces 5, 5 are attached to the support 2a of the knob base 2. Both engaging pieces 5 are pushed by a compression spring 6. Therefore, both engaging pieces 5 can be engaged with recesses formed on the moderation surface 4a. Accordingly, when the knob dial 3 is rotated for operation, both engaging pieces 5 are pushed by protrusions formed on the moderation surface 4a and retracted into the support 2a. After that, they are protruded by a spring force of the compression spring 6 and engaged in the recesses on the moderation surface 4a. Due to the foregoing, a rotary position of the knob dial 3 can be regulated, and it is possible to provide a feeling of moderation in the rotary operation of the knob dial 3.
However, in the above conventional structure, the direction of deflection of the compression spring 6, that is, a moving direction of the engaging piece 5 is different from the pushing direction. Therefore, when both engaging pieces 5 are pushed into the supports 2a, it is necessary to rotate the knob dial 3 with a relatively strong force. Accordingly, there is a tendency that an operator feels high resistance in the operation of the knob dial 3. Further, both engaging pieces 5 are kept in a condition in which they are pushed by the protrusions on the moderation surface 4a. Therefore, the operation feeling at an intermediate position of the knob dial 3 grows too heavy.